Brush spring assembly



April 21, 1970 D. A. 4clcaLLl BRUSH SPRING ASSEMBLY Filed Sept. 23, 1968 2 Sheets-Sheet 1 April 2l, 1970 n D4. cloLLl 3,508,098

BRUSH SPRING vASSEMBLY l f Filed Sept. 23, 1968 k2 Sheets-Sheet 2 ArrQQA/f ys United States Patent O 3,508,098 BRUSH SPRING ASSEMBLY Donald A. Ciolli, Cleveland, Ohio, assignor to The Leece- Neville Company, Cleveland, Ohio, a corporation of Ohio Filed Sept. 23, 1968, Ser. No. 761,543 Int. Cl. H011' 39/40 U.S.b Cl. 310-246 13 Claims ABSTRACT F THE DISCLOSURE A brush spring assembly for a motor or generator in which the brush spring urges the brush against the commutator with a force which, through most of the useful wear life of the brush, increases as the brush is worn away. The spring also exerts a side thrust on the brush to overcome any tendency of the brush to move laterally in the brush holder in a direction tangentially of the commutator.

This invention relates to a brush spring assembly for a commutator-type dynamoelectric machine, such as a generator or motor.

An important object of this invention is to provide a novel and improved brush spring assembly in which the force of the brush spring, urging the brush against the commutator, increases progressively throughout most of the useful wear life of the brush.

Another object of this invention is to provide such a brush spring assembly in which, even though the force of the spring decreases toward the end of the useful wear life fof the brush, the spring force at the end is substantially at least as great as at the beginning of the wear life of the brush.

Another object of this invention is to provide a novel and improved brush spring assembly in which the spring exerts a side thrust on the brush which tends to prevent undesired lateral movement of the brush in its holder, tangentially with respect to the commutator, throughout the useful wear life of the brush.

Further objects and advantages of this invention will be apparent from the following detailed description of a presently-preferred embodiment, which is described with reference to the accompanying drawings in which:

FIGURE l is a partial end elevational view showing a dynamoelectric machine embodying several brush spring assemblies in accordance with the present invention, with one of the brush holders shown partly broken away for clarity; v

FIGURE 2 is a side elevational view of the FIG. 1 machine, partly broken away for clarity;

FIGURE 3 illustrates one 'of the present brush springs in enlarged detail and the relationshipfof its free end to 'the outer end of the brush as the latter becomes wo'rn away; and

FIGURE 4 shows the spring force plotted against the deflection of its free end for various brush positions in one practical embodiment of this invention.

Referring to FIG. 1, the dynamoelectric machine illustrated there' has avconventional segmented rotary commtator made up of a cylindrically-arranged series of cormmutator segments 11, each of which presents a radially-outwardly facing arcuate face for engagement by the inner end face of a brush 12. In the illustrated embodiment, the dynamoelectric machine has four brushes spaced apart at 90 intervals circumferentially around the comv mutator.

Each brush 12 is slidably mounted in a guideway 13 in a brush holder 14, which guideway extends radially of the commutator 10. As best seen in FIG. 2, each brush holder 14 comprises a generally at base plate 15 and a ICC member 16 which is secured to the base plate, such as by spot welding. Member 16 presents a pair of spaced, parallel sides 17 and 18 which extend perpendicularly from' the base plate 15 and are bridged by a wall 19 spaced away from the base plate and extending parallel to itrThe base plate 15 and the sides 17, 18 and the wall 19 together ldefine the brush guideway 13, which is disposed radially with respect to the commutator. The sides 17 and'18 are formed with respective slots 20 and 21 which are open at the outer end of the brush holder and which terminate in respective stop shoulders 22 and 23 (FIG. 1) located inwardly along the brush holder from its outer end (away from the commutator).

Each brush holder has a spring-supporting tab 24 on member 16 which extends perpendicular to the base plate at one side of the brush guideway 13. In the particular embodiment illustrated, this tab is located to the right of the guideway 13, looking radially inward toward the commutator 10. This tab 24 has flat opposite major faces extending at 70 to the length of the brush guideway 13 (which extends radially of the commutator). The tab 24 provides an anchor or support to which the inner end of the spiral, clock-type brush spring25 is snugly attached.

To the right of the brush guideway 13 in FIGS. 1 and 2, the base plate 15 and member 16 of the brush holder present contiguously disposed, offset mounting portions 26 and 27 (FIG. 2). The motor housing 28 presents a boss 29 which threadedly receives a clamp bolt 30 extending through the mounting portions 26 and 27. The clamp bolt clamps the mounting portions 26, 27 of the brush holder against the housing boss 29, and these mounting portions are electrically insulated from the housing boss 29 and the clamp bolt 30 by an arrangement f' of at washers 31-33 and a bushing 34, all of rubber or other suitable dielectric material.

At its opposite end, to the left of the brush guideway 13 in FIGS. 1 and 2, the brush holder members 15 and 16 present offset mounting portions 35 and 36 which are similarly clamped against a boss 37 on the housing.

As shown in FIG. l, the brush spring 25 presents successive spiral turns extending from its mounted inner end and it terminates in a free end portion 25a which extends laterally of the brush guideway and engages the outer end face 12a of the brush at the corner 12b of the latter which is closest to the spring-supporting tab 24. This free end portion 25a of the spring preferably has a reverse curvaturei.e., a curvature opposite to the principal spiral curvature of the spring. For example, as viewed in FIG. 1, the spring 25 has a counterclockwise spiral curvature and the free end portion 25a of the spring has a clockwise curvature, both in the direction outwardly from the mounted inner end of the spring.

In accordance with the present invention the brush spring 25 applies a force on the brush 12, directed radially inward toward the commutator, which increases throughout most of the useful wear life of the brush. This increasing force is considered to be advantageous in increasing the brush life by overcoming the effects of the increasing roughness of the brush-engaging surfaces of the commutator as wear takes place there.

Also, the spring exerts a side force on the brush, tangentially of the commutator 10, which minimizes any tendency of the brush to wobble in that direction.

In the illustrated embodiment of the invention, because of design limitations imposed by the brush holder the radial force applied to the brush by the spring decreases as wear takes place toward the end of the useful wear life of the brush, but not below the force exerted by the spring on a new brush.

FIGURE 4 illustrates the spring force on the brush plotted against the spring deection as 'a result of brush wear. At the right end of this graph the spring force for a new brush is shown as being about 2.6 pounds. As the brush becomes worn in use and the free end portion of the spring moves inwardly along the brush guideway in the direction of the commutator, the force which the spring exerts on the brush radially of the commutator increases gradually up to a maximum value of about 3.5 pounds. This progressive increase of the spring force occurs over about 70% of the useful wear life of the brush, starting from the new brush position. In the final 30% of the brushs wear life, the spring force decreases gradually from the maximum value of 3.5 pounds down to a nal value of about 2.7 pounds at the worn brush position 'at which the brush should be replaced. This worn brush position of the free end portion of the spring is V16 inch outwardly along the brush guideway from the stop shoulder 23 on the brush holder. The zero position of the spring along the abscissa in FIG. 4 is the position in which its free end engages the stop shoulder 23, at which time the spring is stressed such that its free end exerts a force of about 1.9 pounds against this stop shoulder in a direction radially inward with respect to the commutator.

FIGURE 3 shows the brush spring 25 in enlarged detail, with the complete spring being depicted in its unstressed, fully expanded condition.

Position 1 in FIG. 3 is the position of the free end portion 25a of the spring when it engages the adjacent corner 12b on the outer end face of the brush with a new brush installed in the brush guideway 13 and before any wear has taken place on the brush.

Position 2 in FIG. 3 indicates the location of the free end portion of the spring at an intermediate position between positions 1 'and 3, in which the radial distance between the center of the spiral spring and the point of its engagement with the adjacent corner 12b on the outer end face of the brush is a minimum.

Position 3 in FIG. 3 indicates the location of the free end portion of the spring after the brush has been worn away enough to require' replacement.

Position 4 shows the position of the stop shoulders 22 and 23on the brush holder.

The total working angle of the spring is the angle A between position 1, for a new brush, and position 3, where the worn brush is to be replaced. The angle B between positions 1 and 2 occupies the major portion of the total working angle A.

Considering now the action of the spring only during its movement between positions 1 and 2, in position 2 the effective radius alrm of the spring (from its center 0 to the adjacent corner 12b on the outer end of the brush) is r2. Because of the position of the spring-supporting tab 24 on the brush holder with respect to the brush guideway 13, position 2 is the position of the free end portion of the spring in which the effective radius arm of the spring is a minimum.

At 'any other spring position between positions 1 and 2, this radius arm can be expressed as cos b f 12 radially of the commutator is equal to P2 at position 2, then the torque load T on the spring at any other spring position between positions 1 and 2 can be expressed as T T z-l-kb where k is a spring constant (torque per degree).

The force P at this spring position can be expressed as T P-T cos b (3) P: (T2-Hab) coszb In accordance with the present invention, the force P which the spring exerts on the brush should increase. throughout the entire angular range B from position 1 to position 2, and therefore dP/db must always be negative from positions 2 to position 1.

Equation 4 may be rewritten as:

P= (T2 cosZb-I-kb cos2b) throughout the entire angle B. The relationship expressed at (9) above holds true for most of the useful wear life of the brush, in accordance with the present invention.

As indicated by FIG. 4, in the particular embodiment disclosed, toward the end of the wear life of the brush, after the spring has moved past its minimum radius arm position, the force which it exerts on the brush, urging the latter against the commutator, decreases gradually to a final value slightly above the force which it exerts on a new brush. However, where permitted by limitations of space and the design of the brush holder, it will be preferable to arrange the brush spring so that its minimum effective radius arm position is at or close to the worn brush position at which the brush will be replaced, in which case the spring force on the brush will increase progressively throughout the entire useful wear life of the brush.

In addition to the applying to the brush a force directed radially of the commutator which increases progressively for most of the useful wear life of the brush, the brush spring in the present assembly also applies a side thrust on the brush urging it against the opposite side wall of the brush guideway from the corner 12b on the brush. This side thrust is provided throughout the entire useful wear life of the brush (i.e., from position 1 to position 3 in FIG. 3), so as to avoid any tendency for sideward displacement or wobble of the brush in a direction tangentially of the commutator.

The reverse curvature of the free end portion 26 of the brush spring insures that it engages only the adjacent corner 12b on the outer end of the brush and imposes the side thrust on the latter throughout the useful wear life of the brush, `while at the same time minimizing the spacing required between the brush guideway 13 and the mounted inner end of the spring for a desired useful wear length of the brush.

While a presently-preferred embodiment of this invention has been described in detail with reference to the accompanying drawings, it is to be understood that various structural modifications differing from the particular arrangement disclosed may be adopted without departing from the scope of this invention.

Having described my invention, I claim:

1. A brush spring assembly for a commutator-type dynamoelectric machine, said assembly comprising a brush holder having a brush guideway, and a spiral clock-type spring having its inner end mounted at one side of said brush guideway and having a movable free outer end portion extending laterally of said guideway for engagement with the outer end of the brush to urge the latter along the where b ip s the angular displacement of the spring outwardly along the guideway from its minimum effective radius arrnposition, T2 is the torque load on the spring at its minimum effective radius armwposition, and k is a torque-perdegree constant of the spring, so that as the brush becomes worn the spring exerts a progressively increasing force on the brush from th new-brush position of the free epd portion of the springlinwardly along said guideway tio its minimum effective radius arm position.

2. A brush spring assembly according to claim 1, wherein said free end portion of the spring has a reverse curvaturezj 3. A brush spring assembly according to claim 1, wherein said free end portion of the spring throughout its movement'between said new brush position and said minimum effective radius arm position exerts a lateral force on the brush urging the latter against the opposite side of said guideway.

4. A brush spring assembly according to claim 3, wherein said free end portion of the spring has a curvature opposite to the principal spiral curvature of the spring.

5. A brush spring assembly according to claim '1, wherein s aid free end portion of the spring is movable along the brush guideway inwardly past said minimum effective radius arm position to a final worn-brush position, said minimum effective radius arm position being substantially closer to said final worn-brush position than to said new brush position. i

6. A brush spring assembly according to claim 5, wherein said free end portion of the spring throughout its movement between said new Ibrush position and said final worn-brush position exerts a lateral thrust on the brush urging the'latter against the opposite side of said guideway.

7. A brush spring assembly according to claim wherein said free end portion of the spring extends laterally across said brush guideway and has a curvature opposite to the principal spiral curvature of the spring.

8. In afdynameolectric machine having a commutator, an assembly comprising a brush holder having a brush guideway which extends substantially radially inward toward the commutator, a brush sl'idably received in said guidewayand having an inner end engageable with the commutator and an opposite outer end, and a spiral clocktype spring having its inner end mounted on said brush holder atone side of said brush guideway and having a free end portion extending laterally in said guideway for engagement with said outer end face of the brush therein,

said spring being stressed by the engagement of its free end portion with the outer end of the brush in all positions of said free end portion from a new-brush position to a position inwardly along the guideway in which the spring has a minimum effective radius arm with respect to the outer end of the brush, said spring throughout its movement from said new-brush position to said minimum effective radius arm position satisfying the relationship where b is the angular displacement of the spring outwardly along the guideway from its minimum effective radius arm position, T2 is the torque load on the spring at its minimum effective radius arm position, and k is a torque-.per-degree constant of the spring, so that as the brush becomes worn the spring exerts a progressively increasing force on brush from the new-brush position of the free end of the spring inwardl'yalong said guideway to its minimum effective radius arm position.

9. An assembly according to claim 8, wherein said free end portion of the spring has a reverse curvature from the principal spiral curvature of the spring. f

.10. An assembly according to claim 8, wherein said free end portion of the spring throughout its movement between vSaid new-brush position and said minimum effective radius arm position exerts a lateral force on the brush urging the latter against the opposite side of said guidefway.

11. An assembly according to claim 8, wherein said free end portion of the spring is movable along the brush guideway inwardly past said minimum effective radius arm position to a final worn-brush position, said minimum effective radius arm position being substantially closer to said final worn-brush position than to said new-brush position. f

12. An assembly according to claim 11, wherein said free end portion of the spring throughout its movement between said new-brush position and said final worn-brush position exerts a lateral thrust on the brush urging the latter against the opposite side of said guideway. f

13. An assembly according to claim 12, wherein -said free end portion of the spring has a curvature opposite to the principal spiral curvature of the spring.

References Cited UNITED STATES PATENTS 777,709 12/ 1904 Woehr 310-246 2,900,540 8/ 1959 Gartner et al. S10-246 2,972,689 2/1961 Kuhn 3l0-246 3,132,273 5 1964 Pernetta 310-246 3,423,618 1/1969 Schmid et al 310-246 3,231,772 l/ 1966 Polenschat 310l-246 MILTON O. HIRSHFIELD, Primary Examiner L. L. SMITH, Assistant Examiner 

